Isocyanate-blocked, mercaptan-functional organic polysulfide polymers, and their stable and curable admixtures with curing agents therefor



United States Patent 3,361,720 ISOCYANATE-BLOCKED, MERCAPTAN-FUNC-TPZONAL ORGANIC POLYSULFIDE PGLY- MERE, AND THEE! STABLE AND CURA- BLEADMIXTURES WITH CURING AGENTS THEREFGR Eugene R. Bertozzi, Yardley, Pa,assignor to Thioisoi Chemical Corporation, Bristol, Pa, a corporation ofDelaware No Drawing. Continuation of application Sci. No. 383,917, July20, 196%. This application Jan. Ill, 1967, Ser. No. 693,461

Claims. (Cl. 260-775) ABSTRACT OF THE DESCLOSURE This disclosure relatesto novel polymers, i.e., polysulfide polymers with mercaptan terminalsblocked by monofunetional isocyanate compounds; the process forpreparing such blocked polymers, and storable compositions containingsuch blocked polymers and curing agents.

The present invention relates to the organic polysulfide polymer art. Inparticular, the present invention relates to novel polysulfide polymercompositions and the process for their preparation whereinmercaptan-functional polysulfide polymers have their reactive mercaptangroups blocked by monofunctional organic isocyanates to form heatsensitive isocyanate-capped mercaptan group containing organicpolysulfide polymers. This invention further relates to novel curableand time-stable admixtures of such capped polysulfides and curing agentsof mercaptan-functional polysulfide polymers, and to the process fortheir preparation. This invention especially relates to such admixtureswhich comprise bin-stable polysulfide crude rubbers and curing agentstherefor.

An object of this invention is to provide novel isocyanate-blockedmercaptan-functional polysulfide polymers and a novel method for theirpreparation.

Another object of this invention is to provide curable and stableone-package compositions of mercaptan-functional polysulfide polymersand curing agents therefor, and a novel method for their preparation.

Still another object of this invention is to provide binstable curablecompositions of mercaptan-functional polysulfide crude rubbers inadmixture with curing agents therefor.

Other objects of this invention are apparent from or are inherent in thefollowing explanations and examples.

It has been expectedly discovered that the foregoing objects of thepresent invention are achieved through the preparation of novelisocyanate-blocked polysulfide polymers prepared by the reaction ofmercaptan-functional polysulfide polymers with monofunctionalisocyanates, and by the admixture of these blocked polymers with curingagents therefor.

Mercaptan-functional polysulfide polymers of the type disclosed in thePatrick and Ferguson patent, U.S. 2,466,963, are now well known in theart and have been extensively used for a variety of commercialapplications, and when cured to form rubber-like solids, possess anumber of commercially important properties. They are inert to oil, mostsolvents, water, mild acids and alkalies, as well as to ozone andsunlight. They are tough and resilient and retain their flexibility atextremely low temperatures. Moreover, they are impermeable to gases andmoisture, and are capable of adhering tenaciously to such diversematerials as glass, metals, plastics, wood, leather, and fabrics.Because of these valuable properties, they have been extensively used asimpregnating, sealing, caulking, and coating materials, as well as for avariety Patented Jan. 2, 1968 of uses such as to make gasoline hose,printer rolls, and potting compounds for electrical components.

Polysulfide polymers are characterized by recurring linkages of the type'QSg)" between organic radicals having at least two primary carbon atomsfor connection to the polysulfide linkages, where x is a number greaterthan one and usually not exceeding four, and most preferably two. Thus,for example, where x is 2, disulfide polysulfide mercaptan-functionalorganic polymers may be designated by general structures correspondingto the formula (HS-)JRSSi Ri-SH) d in which the R s may be the same ordifferent, as in the case of copolymers, and are organic radicals whichhave free valence bonds equal to one of the integers 2, 3, and 4. Suchfree valence bonds are attached to diiferent carbon atoms on the radialR. Particularly useful classes of such R radicals are the alkyleneradicals such as the ethylenically unsaturated aliphatic hydrocarbonradicals, the saturated aliphatic oxahydrocarbon radicals andthiahydrocarbon radicals, and the araliphatic hydrocarbon radicals inwhich the free valence bonds are in the aliphatic portion. A morecomprehensive exposition of the specific types of useful R radicals isgiven in Tables I and II of U.S. Patent 2,789,958, which patent isincluded herein by reference. Such radicals may be generallycharacterized as intervening polyvalent organic radicals. The mostpreferable R radicals are predominantly alkylene, such as tCH CHfi andtCil illi Cl-l ci-l -l, oxahydrocarbon, such as tCli Cii OCH ci-ifi and{-CH CH OCH OCH CH2); and copolymeric Rs of alkylene and oxahydrocarbongroups separated by 8 groups. In the polymer formula above, it is anumber greater than 3 and large enough, and depending in good measureupon the nature and weight of the R groups, to provide a polymer with amolecular weight of at least 500. It may vary, in the case of liquidpolymers, from. about 3 to about 100, to provide polymers with molecularweights of about 500 to 12,000, that is, polymers that are normallyliquids at about 25 in the case of solid polysulfide polymers, n mayvary from about to several thousand to provide polymers with molecularWeights in excess of about 12,000 to several million. In the formula,the sum c+d is the average number of reactive mercaptan groups perpolysulfide polymer molecule.

The mercaptan-functional polysulfide polymers which are commerciallyimportant are preferably formed by reaction of an organic dihalide,having an organic portion corresponding to the aforementioned Rradicals, with an inorganic polysulfide M(-S,;) M being a cationicspecies, preferably an alkali metal or alkaline earth metal, and oftenin the presence of a relatively minor amount, usually not in excess ofabout 4% by weight, of a polyfunctional crosslinking agent such astrichloropropane. The resultant solid latex-like polymers may, in thecase of liquid products desired, be extensively split, or in the case ofcrude rubber products desired, be split in a more limited degree by theprocess of Patrick and Ferguson, U.S. Patent 2,466,963, which patent isincluded herein by reference. This latter patent lists a number of otherpatents which are also included herein by reference and which provideextensive descriptions of the formulation of solid mercaptan-functionalorganic polysulfide polymers such as latex-like materials and cruderubbers. The polysulfide polymers that are useful in the presentinvention, therefore, are those with molecular weights from 500 toseveral million, and which have a plurality of reactive mercaptangroups, e.g. the sum c+d, of at least an average of 1.5, and preferablyabout 2 to 10 per polymer molecule, and at most an average of 12, andwhich therefore span the range of liquid polysulfide polymers to 3polysulfide crude rubbers. Mixtures of the solid and liquid polymers maybe used according to the present invention as well as either of the twotypes alone.

The polysulfide polymers useful in the present compositions and processare polysulfide polymers, as disclosed above, which are curable; that isto say, they have a plurality of reactive mercaptan groups which arecapable of undergoing condensation and/or crosslinking and/ or chainextension reactions to provide a substantially stable rubbery solid.These reactions are usually induced by compounds which are called curingagents, and which themselves form connecting bridges between polysulfidemolecules at sites of the reactive mercaptan groups, and thus becomepart of the polymetric matrix; or they may merely induce reactionbetween reactive mercaptan groups on adjacent polysulfide molecules toprovide condensation and/ or crosslinking and/ or chain extensionbridges between said molecules at the mercaptan sites. The types andnatures of such curing agents have been extensively studied and many arewell known such as the metal oxides, chromates, dichromates, etc. andthe organic oxidizing agents, sulfur, air, oxygen, epoxides, etc. All ofthese are usefully employed in the compositions of the presentinvention.

In general, the admixture of or contact of mercaptanreactive-group-containing polysulfide polymers with curing agentstherefor, upon such admixture or contact, will produce chemicallydynamic systems which undergo the aforesaid crosslinking and/ orcondensation and/or chain extension reactions, commonly known as curereactions, ultimately to produce with time solid crosslinked polysulfiderubbers. These systems, as has been indicated, are in a state ofreaction, and as such do not have long-termed stability as workablecurable admixtures. It is a usual practice, therefore, to admix curingagents with the polysulfide polymers just prior to the time when it isdesired to obtain the cured polysulfide rubbers. Cure reactions, ingeneral, depend on the type of polysulfide polymer, its mercaptanfunctionality, and the type and functionality of the curing agent, andproceed at temperatures which extend from common ambient temperatures,say about 60 to 90 F., to about 350 F. Even at such ambient temperaturesas those commonly prevalent during storage of materials, e.g. 40 to 120F., prior art admixtures of mercaptan-functional polysulfide polymersand curing agents therefore will to some degree cure and becomeunworkable within relatively short intervals, even in instances wheresuch prior art systems at such temperatures usually require longintervals to fully cure to elastomers. It has been long desired in theart to have curable admixtures of polysulfide polymers and their curingagents in so-called one-package systems which may be stored at ambienttemperatures for extended periods of time without substantial change intheir workability and curable properties or bin stability. Until theadvent of the present invention, this has not been possible.

In general, according to the present invention, the foregoing definedpolysulfide polymers are reacted with monofunctional organic isocyanatesto provide polysulfide polymers with isocyanate-blocked mercaptangroups. Curable admixtures of such blocked polymers may then be preparedwith curing agents, which admixtures do not change substantially incurable properties over extended periods of time, often exceeding ayear; and at the time desired for the forming of a polysulfide rubberthe present admixtures may then be cured thereto at elevatedtemperatures of about 200 to 450 F. in about 0.1 to 50* hours.

The reactivity of the polysulfide polymers depicted by usectas a R{-SH)is importantly dependent upon the average number of mercaptan groupsavailable for reaction, that is to say the sum c-l-d; this average sumis greater than one, and may be only fractionally greater, say 1.5 or1.8, and yet still provide enough molecules with 2, 3, or even 12mercaptan groups topermit vulcanization to rubbers with excellentproperties. In

general, the preferred average sum c+d is about 2 to 10, and not lessthan about 1.5 to not more than about 12.

isocyanate-blocked organic polysulfide polymers of the present inventionare prepared by the reaction of monofunctional organic isocyanate withmercaptan-functional polysulfide polymers, as defined above, inaccordance with the equation depicted as follows:

The blocking reaction is conducted at elevated temperatures aboveambient of about toabout 225 F., in about 0.1 to about 10 hours. Ingeneral, the blocking reaction is to be conducted in the absence ofmaterials which would be reactive with either mercaptan groups or withisocyanate groups, such as epoxides, water, alcohols, etc. It isdesirable, therefore, to conduct the reaction in a relatively dryatmosphere, which is to say essentially devoid of water or water vapor,and to provide reactants which in themselves do not contain foreignsubstances, such as water, which would react with mercaptan orisocyanate.

Monofunctional isocyanates which are useful in the practice of thepresent invention may be generally desig-.

nated as those having a formula depicted by RNCO, wherein R is amonovalent grouping that may be alkyl, aryl, alkaryl, or aralkyl innature. Typical useful monofunctional organic isocyanates include, amongthe alkyl isocyanates, methyl isocyanate, ethyl isocyanate, propyl andisopropyl isocyanate, n-butyl isocyanate, octyl isocyanate, dodecylisocyanate, etc.; and among the aryl isocyanates one may include phenylisocyanate, 2-naphthyl isocyanate, p-ethoxyphenyl isocyanate,p-bromophenyl isocyanate, o-chlorophenyl isocyanate, m-chlorophenylisocyanate, p-chlorophenyl isocyanate, o-ethoxyphenyl isocyanate,o-nitrophenyl isocyanate, 2-biphenyl isocyanate, m-nitrophenylisocyanate, 4-biphenyl isocyanate, o-naphthoxyphenyl isocyanate,p-methoxyphenyl isocyanate, pphenylazophenyl isocyanate, etc. The mostuseful monofunctional isocyanate presently found in the practice of thepresent invention is phenyl isocyanate. As may be seen from theforegoing equation, in order to provide completely blocked polysulfidecompositions of the present invention, it is desirable to employ atleast stoichiometrically reactive amounts of the monofunctionalisocyanate with the mercaptan-functional polysulfide polymer usedwherein a-t-b equals at least c-t-d. In order to insure such completeblocking, it is often desirable to employ at least a slight excess ofthe isocyanate. Thus, if one mole of a difunctional mercaptan-functionalpolysulfide polymer is used, at least two moles of the isocyanatecompound are required for complete blocking; and if the polysulfidepolymer is pentafunctional, at least five moles of the isocyanatecompound are then required for complete blocking. It is alsocontemplated, according to the practice of the present invention heretaught, that partially-blocked polysulfide polymers, which may proveuseful for specific end uses, may also be prepared according to thepresent process. To provide such partially-blocked polysulfide polymers,therefore, one would use less than a stoichiometric amount of isocyanatewith the amount of mercaptan functional polysulfide used. The mostuseful partiallyblocked polysulfide polymers of the present inventionhave at least 50% of their mercaptan groups blocked, e.g. where a+bequals at least one-half c-l-d in the equation. Where substantially lessthan 50% blocking occurs, the stability of curable compositions formedwith curing agents therefor is sharply reduced, and approaches that ofthe prior art curable compositions.

In general, the stability of the present curable admixture compositionsis importantly dependent upon not only the proportion of monoisocyanateused per mole of mercaptan-functional polysulfide polymer, but also uponthe molecular wei ht of the polysulfide polymer, e.g. at least 500 forstable compositions, its functionality, the nature of R and R, and thenature of the adjuvants and impurities that may be present in thecurable admixture compositions of the present invention. At any event,the stability of the present admixture compositions is substantiallygreater than that of otherwise identical compositions in which thepolysulfide polymers have not been at-leastpartially blocked withisocyanate.

The nature of curing agents which may be admixed with the presentblocked polysulfide polymers to form the present curable and stableadmixtures, has been alluded to above. Among the more useful curingagents for liquid polysulfide polymers, say of molecular weight fromabout 500 to 12,000, may be included Sb O Mg TeO SeO MnO Mn0 coated withmauganite, PbO organic peroxides, nitro-aryl compounds, etc. Curingagent systerns for relatively high molecular weight polysulfidepolymers, including the solid polymers such as crude rubbers, inaddition to the aforementioned curing agents, include such compositionsas zinc oxide, quinone dioxime, tincture of iodine, calcium oxide, andthose other curing agents listed in the various patents included hereinby reference.

The foregoing curing agents are used according to the present invention,individually, or in combinations of more than one, in quantitiessufiicient to substantially oxidize all of the mercaptan groups, aspresent in the polysulfide polymers prior to blocking. In general,amounts of curing agents useful to provide such substantially completeoxidation may vary from about 0.5 to in excess of 20 parts by weight per100 parts by weight of the polysulfide polymer to be cured. To effectcures of the present admixtures, which are prepared merely by admixtureas on a mill to provide an intimate and uniform blend of the blockedpolysulfide polymers and the curing agents therefor, substantialunblocking of the blocked polymers is required. This may be depicted bythe following equation:

0 o H l r l H NHC s \RSX/ R s CHN R A (Es) sx/u R sH b (a+ Unblockiugrequires elevated temperatures above ambient, usually above thevolatilization temperature of RNCO, and usually falling into the rangeof about 200 to about 450 F. for about 0.1 to about 5 hours. At theseelevated temperatures, as soon as the unblocking reaction occurs, thenewly reconstituted mercaptan groups will react under the influence ofthe curing agents to provide the necessary condensation and/ orcrosslinking and/ or chain extention reactions, known as curing orvulcanization reactions, which provide solid cured rubbery polymers.These curing reactions are permitted to proceed at the foregoingtemperatures until such time as stable rubbery vulcanizates areproduced.

The following examples illustrate modes of practice to prepare thecompositions, and to conduct the processes of the present invention, butare not intended to impose limitations upon the scope of the inventionwhich is defined in the appended claims.

Example 1.Preparation and cure of IBLP-3, an isocyzmate-blacked liquidpolysulfide polymer of about 1000 molecular weight A 2-liter, B-neckedreaction flask fitted with stirrer, condenser with drying tube open tothe atmosphere, and a gas admission tube for providing a blanket of drygas therein, was sequentially charged with agitation with 1 mol of LP- 3polymer, a liquid dimercaptan-functional polysulfide polymer ofmolecular weight of about 1000, previously dried of water, having as itsrepeating unit and having a 2% crosslink provided by trichloropropane,and with 2.2 mols of phenyl isocyanate under a blanket of dry nitrogengas. The reaction mixture was elevated to 192 to 203 F. and maintainedthere for about 5 hours and then cooled to ambient to provide IBLP-3, anisocyanate-blocked liquid polysulfide polymer of this invention. IBLP3was of similar color but slightly more viscous than LP-3 polymer.

The blocked liquid polysulfide polymer IBLP-3 was uniformly admixed withlead dioxide, a curing agent for mercaptan-functional polysulfidepolymers, in quantity of 7.5 parts by weight per p.b.w. of polymer. Thecurable composition was permitted to stand at ambient temperatures ofabout 75 F. and at the end of at least 16 hours no perceptible signs ofcure, such as thickening of the composition, was observed. Admixtures ofprior art non-blocked mercaptan-functional polysulfide liquid polymersand lead dioxide of otherwise identical constitution to the presentcomposition completely cured to form solid rubbers at about 75 F. infrom 1 to at most 4 hours. The present composition was then heated atabout 212 F. for about 30 minutes to provide a fully cured rubberypolysulfide vulcanizate.

Example 2.,Preparati0n of IBLP-Z, an isocyanateblocked liquidpolysulfide polymer of about 4000 molecular weight In similar manner toExample 1, 1 mol of LP-2 polymer, a dimercaptan-functional polysulfidepolymer sim ilar to LP-3 polymer in all ways but having a molecularweight of about 4,000, was reacted with about 2.2 mols of phenylisocyanate to provide IBLP-2, an isocyanateblocked liquid polysulfide ofthis invention that was of similar color but more viscous than LP-Zpolymer. IBLP- 2 in admixture with curing agents was capable oflongtermed stability at ambient storage temperatures, and cure to afully vulcanized rubber at temperatures of about to 400 F. within 0.1 to6 hours.

Examples 3 to 12.Preparation and cure of IBS T CR, an isocyanate-blockedpolysulfide crude rubber Mercaptan-functional polysulfide crude rubbers,which usually have molecular weights in excess of 100,000 to about 2million have relatively poor bin-stability, which is to say that uponrelatively short-termed storage either in admixture with curing agentstherefor or even in contact with air, the oxygen of which acts as a slowcuring agent therefor, the rubbers will cure to the degree that they canno longer be worked on a mill so as to permit admixture with necessarycompounding ingredients, and cannot be formed to the shape of enddesired vulcanized articles. In essence they lose the neededpiezo-thermoplasticity to be worked prior to cure.

In the following examples, a decyl-mercaptan-functional polysulfidecrude rubber designated STCR, formed with repeating units of {-C H OCHOC H SS9- and a 2% crosslink imparted by trichloropropane, wascompounded With various ingredients on a rubber mill at ambienttemperatures, and observed as to its bin stability. In Example 3, nocuring agents were used. In Examples 3, 5, 7, and 9, a small quantity ofIBLP-3, prepared as in Example 1 was added, which contained enough freeexcess phenyl isocyanate from the blocking step to substantially blockall of the mercaptan groups of the STCR crude rubber. In Examples 4 to 9sundry curing agents and mixtures were used, and are designated in thetable of example as C1, which is quinone dioxime (GMF), C-2, zinc oxide,

C-3, 2% tincture of iodine and C4, lead dioxide.

7 A portion of each of the milled rubber stocks was stored at ambienttemperatures and observed daily for loss of workable properties, or binstability. Another portion of the milled stocks was cured at 287 F. for30 minutes to 8 n is a positive number sufficient to provide saidpolysulfide polymer with a molecular weight of at least 500; x is anumber greater than one and not substantially exceeding four;

be tested for vulcanizate properties.

To prepare the stocks, two masterbatches were prepared R is a monovalentorganic group selected from the on a rubber mill according to therecipes: class of monovalent organic groups consisting of alk 1, ar 1alkar l and aralk l monovalent rou s" Masterbatch A: y y y g P STCRp.b.w 100 19 R 18 an intervening organic radical having a valenceStearic acid p.b.w 1 1 f h 0 2 3 d 4 d I d Carbon black, SRF #3 60 equato one o t e inte ers an an 18 se ecte from the group of organicradicals selected from the Masterbatch B: 1 group consisting of aikyleneradicals, ethylenically un- ST CR p.b.w 97 saturated aliphatichydrocarbon radicals, saturated all Stearic acid p.b.w 1 phaticoxahydrocarbon and thiahydrocarbon radicals, Carbon black, SRF #3 p.b.w60 and araliphatic hydrocarbon radicals in which the IBLP-3 p.b.w 3valences are in the aliphatic portion.

7 2. A monofunctional isocyanate blocked mercaptan- The masterbatcheswere then heated for about 24 hours functional polysulfide polymeraccording to claim 1 which at about 200 F. to remove traces of moisture,and to aid is normally a liquid polymer at C. in completion of theblocking of the crude rubber in 3. A monofunctional isocyanate blockedmercaptan- Masterbatch B. The masterbatches were then cooled tofunctional polysulfide polymer according to claim 1 which ambient. Theaforesaid curing agents were then milled into is normally a solidpolymer at 25 C. the masterbatches at ambient temperatures in the quan-4. A monofunctional isocyanate blocked mercaptantities listed in thetable of examples to provide curable functional polysulfide polymeraccording to claim 1 wherecompounded crude rubber stocks. A portion ofeach stock in said R is a phenyl group. was stored at ambienttemperatures and observed daily for 5. A monofuuctional isocyanateblocked mercaptanloss of bin stability. Another portion was vulcanizedto functional polysulfide polymer according to claim 1 whereprovidecured rubbers with properties as listed below. in said number a-i-b isequal to at the least said number I claim: c-l-d. I 1. A monofunctionalisocyanate blocked mercaptan- 6. A monofunctional isocyanate blockedmercaptan- Example Recipe, in parts by weight (p.b.w.):

Type of masterbatch 1 B l A a B A B A B Amount of masterbatch 161 161161 161 161 161 Type of curing agent 01 & 2 C1 & 2 02 & 3 C2 & 3 04 04Amount ofcuring agent. 0.0 1 5 & .5 1.5 & .5 1.5 dz .5 1.5 & .5 3 3Uncured stocks:

Bin stability, in days 500 66 500 17 500 3 491 Mooney viscosity, ML-4 2initial upon preparation 25 Vuleanizate Properties:

Tensile strength, in p.s.i. 1, 100 850 1, 200 1, 100 1, 190 960 Ultimateelongation, in p.s.i. 300 360 390 420 250 310 Hardness, in Shore Adurometer degrees 58 64 59 68 62 1 As in text. 2 Test method ASTMD-1646-53T. 3 Test method ASTM D-41251T. 4 Test method ASTM D-676-59T. 5No cure. 2 p.b.w. of stearic acid added to recipe.

functional organic polysulfide polymer corresponding to functionalpoiysulfide polymer according to claim 1 wherethe formula: in said R is{C H OCH OC I-k).

7. A monofunctional isocyanate blocked mercaptani f f H functionalpolysulfide polymer according to claim 1 where- (R'-NHo-s \RS,/R\S--CHNR in said x is about 2.

a n b 60 8. A monofunctional isocyanate blocked mercaptanwher functionalpolysulfide polymer according to claim 1 wherein said a-l-b is about 2.8 P Q Y number equal to F 163st One-half -i- 9. A monofunctionalisocyanate blocked mercaptan- POSIUVe numb exceedlng P and notfunctional polysulfide polymer according to claim 1 wherestantiallygreater than twelve and IS the number of (35 in Said is about mefcaptaflgroups of the Organic Poll/Sulfide Polymer 19. A process for preparing amonofunctional-isocyacorfespofldmg t0 the formula nate blocked mercaptanfunctional organic polysulfide polymer comprising the steps of o' x)n )d(i) admixing to uniform admixture at least one un- V 70 blockedpolysulfide polymer of the formula which organic polysulfide polymer hasbeen reacted with an organic monofunctional isocyanate compound to formsaid monofunctiona l-isocyanateblocked mercaptan functional organicpolysulfide polymer;

c+d is a positive number exceeding one and not substantially exceedingtwelve,

R is an intervening organic radical having a valence equal to one of theintegers 2, 3, 4, and is selected from the group of organic radicalsselected from the group consisting of alkylene radicals, ethylenicallyunsaturated aliphatic hydrocarbon radicals, saturated aliphaticoxahydrocarbon and thiahydrocarbon radicals, and araliphatic hydrocarbonradicals in which the valences are in the aliphatic portion,

x is a number greater than one and not substantially exceeding four, and

n is a positive number sufiicient to provide said organic polysulfidepolymer with a molecular weight of at least 500, with an organicmonoisocyanate of the formula RNCO wherein R is a monovalent organicgroup selected from the class of monovalent organic groups consisting ofalkyl, aryl, alkaryl, and aralkyl monovalent groups, and wherein saidisocyanate is present in a quantity of a+b mols per mol of saidpolysulfide polymer, and further wherein said number a-i-b is equal toat least one-half the number c-l-d,

(ii) heating said admixture to a temperature of about 150 to 225 F. forabout 0.1 about hours to provide monofunctional isocyanateblockedmercaptanfunctional organic polysulfide polymer,

said steps (i) and (ii) being conducted under substantially anhydrousconditions, and

(iii) cooling to temperatures below 150 F. said monofunctionalisocyanate blocked mercaptan functional organic polysulfide polymer.

11. A process according to claim 10 wherein said unblocked organicpolysulfide polymer is normally a liquid polymer at 25 C.

12. A process according to claim 10 wherein said unblocked organicpolysulfide polymer is normally a solid polymer at 25 C.

13. A process according to claim 10 wherein said at least one unblockedorganic polysulfide polymer is a mixture of at least on liquidpolysulfide polymer, and at least one solid polysulfide polymer.

14. A process according to claim 10 wherein said at least onemono'functional-isocyanate-blocked mercaptanfunctional organicpolysulfide polymer is a mixture of at least one liquidisocyanate-blocked mercaptan-functional polysulfide polymer and at leastone solid isocyanate-blocked mercaptan-functional polysulfide polymer.

15. A process according to claim 10 wherein said number a-l-b is equalto at least c+d.

16. A process according to claim 10 wheerin said R is rc n ocn oc ua.

17. A process according to claim 10 wherein said R is a phenyl group.

13. A process according to claim 10 wherein said x is about 2.

19. A process according to claim 10 wherein said a-l-b is about 2.

20. A process according to claim 10 wherein said (1+!) is about 10.

21. A method for preparing a storage-stable curable polysulfide polymeradmixture composition comprising the steps of (A) Preparing at least onmonofunctional-isocyanateblocked mercaptan-functional organicpolysulfide polymer according to the steps of claim 36, and

(B) admixing to uniform admixture with said polymer at least one curingagent for mercaptan-functionai organic polysulfide polymers in suchquantity as to provide for substantial oxidation of the mercaptan groupsas present in the mercaptan-functional polysulfide polymer employed inthe preparation of said isocyanate-blocked polysulfide polymer.

22. A method according to claim 21 wherein said quantity of curing agentis from about 0.5 to 20 parts by weight of said curing agent for eachparts by weight of said monofunctional-isocyanate-blocked mercaptanfunctional polysulfide polymer.

23. A method according to claim 21 wherein said at least one curingagent is lead dioxide.

24. A method according to claim 21 wherein said at least one curingagent is quinone dioxime.

25. A method according to claim 21 wherein said at least one curingagent is zinc oxide.

References Cited UNITED STATES PATENTS 2,466,963 4/1949 Patrick et al26079.1 2,676,165 4/1954 Fettes 26079.1 2,764,592 9/1956 Seeger et al.260453 2,789,958 4/1957 Feltes et al. 26079.1 2,814,600 11/1957 Mitchell26077.5 3,282,902 11/1966 Panek 26079 3,201,372 8/1965 \Vagner 260453OTHER REFERENCES Gaylord: Polyethers, Part HI, Interscience Publishers,1962, pp. 75, 82 and 83.

DONALD E. CZAJA, Primary Examiner.

LEON J. BERCOVITZ, Examiner.

M. I. MARQUIS, Assistant Examiner.

